Hydraulic isochronous-droop governor



1966 F. E. SCHEIDLER ETAL 3,279,483

HYDRAULIC ISOCHRONOUS-DROOP GOVERNOR Filed May 25, 1964 FIGJ F|G 3/d4 PI 6 2 mocmewvous 1w Z/NE' Q 90 Q 80 70 1 60 50 A. k 40 E 30 K) /0 P aqaap 1/4/5 R %-5P0 RPM ATTORNEY United States Patent HYDRAULIC ISOCHRONOUS-DROOP GOVERNOR Frederick E. Scheidler, West Hartford, Conn., and Charles F. Stearns, East Longmeadow, Mass., assignors to United Aircraft Corporation, East Hartford, Conn., a

corporation of Delaware Filed May 25, 1964, Ser. No. 369,849 7 Claims. (Cl. 137-35) This invention relates to governors and particularly to mechanism for changing the functioning of a governor between isochronous and droop or proportional governing.

An object of this invention is mechanism including a droop valve and an integrating valve which will automatically, at a preselected speed, change the governor from a droop or proportional governor to an isochronous governor and establish a hydraulic fluid pressure as the governing output signal.

A further object is mechanism including a droop valve and an integrating valve serially connected to each other which will, at a preselected value or control position, change an isochronous governor into a droop or proportional governor.

A still further object is mechanism for disabling the integrating valve so that the droop valve will produce a hydraulic pressure commensurate with the governor.

These and additional objects and advantages will be apparent from the following specification and accompanying drawings in which:

FIG. 1 is a schematic showing of mechanism incorporating the invention.

FIG. 2 is a graph illustrating the operational characteristics of the mechanism of FIG. 1.

FIG. 3 is a schematic showing mechanism for introducing other variables to the system.

This mechanism has been devised to automatically schedule the change from isochronous governing to droop governing or vice versa and has been shown as incorporated in a fuel control device for purpose of illustration. The device schedules the transition as a function of speed (r.p.m.) and the fuel flow required. Droop and isochronous governors are defined as follows:

Droop governora governing device which governs by increases in r.p.m. from a set value, decreasing fuel flow Isochronous governor-a governing device which holds a set speed regardless of fuel flow requirements Now referring to the curves shown in FIG. 2, and tracing the types of governors, first considering the droop type of governor. Assume the governor is set at 82 percent speed at a low condition which would require a steady-state line 0. This condition requires a fuel flow of 48 percent. Now, if the load changes so that the new steady-state operating line is now P, the speed must increase to reduce fuel flow. Since 48 percent fuel flow is too much fuel flow for a new operating line, the engine will increase speed. The droop governor will reduce fuel flow along the droop line until an intersection with the new operating requirements is established. So, from the set value of 82 percent speed, the change in load in creased the speed to 85 percent before an equilibrium point was reached.

The isochronous governor, on the other hand, would have accomplished the required change in fuel flow without any change in speed. This ability to hold the constant speed is the chief advantage which an isochronous governor holds over a droop type governor. To make an isochronous governor stable, it must be made to act slowly. The droop governor, on the other hand, is a more stable and simpler device. The ability of the droop governing device to act rapidly and stably is one of the big advantages that the droop governor has to its credit.

There are jet engine characteristics that make it very desirable to have droop governing during certain speeds particularly at idle and isochronous governing at higher speeds. Again, referring to FIG. 2, the transition device allows isochronous governing at any speed intermediate the transition lines and droop governing at speeds above the top transition line and below the bottom transition line. It will be noted, however, that isochronous and droop governing may occur at the same speed, depending upon the load imposed on the engine or when the engine is undergoing a transition from acceleration to steadystate governing. An example showing the latter condition may be had by referring to the US. application Serial No. 337,904, filed on January 15, 1964, and assigned to the same assignee.

Considering in detail the structure chosen to illustrate this invention, the flyballs 10 are rotated about the axis 12 in timed relation with the engine or device, not shown, whose speed is controlled by the fuel of throttle valve 14 positioned by the governor and controlling the flow of fuel to the engine. Centrifugal force acting on the flyballs 10 cause them to rotate about their pivot 13 for positioning the servo pilot valve 16 which, in turn, varies orifice 18 serving to establish a pressure in line 20 which is a function of the actual speed sensed thereby. This is accomplished by metering supply pressure generated by the pumps 22 and flowing through pipe 24. The metered pressure in line 20 is then directed to the droop valve generally indicated by numeral 26 and the integrating valve generally indicated by numeral 28.

Considering for the moment the details of droop valve 26 which comprises a spool member 29 having a pair of lands 30 and 32 and a fluid reaction surface 36. Spring 38 abuts against one end of spool 28 and fluid pressure fed to the opposing end acts on fluid reaction surface 36. A screw adjustment 40 may be incorporated to adjust the height of spring 38 which, in essence, establishes the droop characteristic which will be more fully appreciated from the description to follow.

Integrating valve 28 comprises a spool 42 which is free floating in its cylinder. The maximum displacement of spool 42 is governed by the set screws 44 and 46 which act as stops. This spool carries metering land 48 and :a pair of reacting surfaces 50 and 52 located on either end. It will be appreciated that spool 42 serves as an integrator when it is spaced from either of the stops 44 or 46 and it moves when flow is caused to enter or leave chamber 52. That is to say, that spool 42 will translate at a velocity that is proportional to the flow generated by upsetting the pressure balance in the hydraulic circuits connecting to the valve end chambers 51 and 53. This is accomplished by providing orifices 56, 58, 60 and the variable orifices defined by land 32 cooperating with its adjacent port. The areas of orifices 56 and 58 are sized to define a pressure which is equal to one-half the value of the pressure in line 20. The area of orifice 60 is fixed and the area defined by land 32 varies to control the pressure on surface 52. When the relationship of the two areas is such that the pressure intermediate thereof is equal to one-half the pressure upstream of orifice 60, spool 42 will cease movement and become balanced. Since this pressure is identical to the pressure in line 20, its value, therefore, is equal to the value intermediate orifices 56 and 58. Whenever reaction surfaces 50 or 52 sense a differential pressure, it will translate as a function of this difference. Since the velocity of spool 42 is a function of the flow int-o or out of the end chambers which, in turn, results from a pressure unbalance, it may be said that this valve integrates the error signal; hence, it is considered an integrating valve.

Next, considering the operation of the droop governor. Flyballs is in reality a speed sensor which positions a servo valve to create a pressure proportional to the speed sensed. This pressure then is fed to orifice 64 disposed in line 66. A portion of the fluid downstream of orifice 6-4 is vented to drain through branch line 68, the speed selector valve 70 and through either of the vent passages 72 or 74 depending on the particular setting of the speed selector valve. The other portion is fed to the underside (reaction surface 36) of droop valve 26. It will be appreciated that this pressure downstream of orifice 64 is, in essence, a speed error signal; namely, the value between the pressure created by the speed selector 70 and the pressure created by flyballs 10.

The desired speed is selected by positioning lever 76 which, in turn, positions rotary valve 70. Rotary valve sets up a venting area between its cooperating ports to meter fluid to vent passage 72 and/or vent passage 74. This area controls the pressure drop across orifice 64 and establishes the desired pressure; namely, the pressure that is equivalent to the desired speed of the engine. For a more detailed description of the speed selector device reference is hereby made to patent application entitled Speed Setting Mechanism and Trimming Means Therefor recently filed in the Patent Office and assigned to the same assignee. Now, consider the effect that droop valve 26 and and integrating valve 28 have upon regulating the throttle valve 14.

Assume, for the moment, that the speed selected is 82 percent and that the throttle valve is regulating sufiicient fuel to run the engine at its equilibrium point on the steady-state line 0. At this point spool 42 of integrating valve 28 will be in the far left position abutting against stop 44. Now, consider the case when the load on the engine for some reason has decreased a particular value. This has the tendency of raising the speed of the engine and causing the flyballs 10 to pivot outwardly about pivot point 13. This causes spool 16 to move to the right for opening the variable orifice 18 which, in turn, increases the pressure in line 20. This pressure fluid is then fed to droop valve 26. Fluid reaction surface 36, feeling the increased pressure, causes spool 28 to shift to the left so that land 30 uncovers its cooperating port. Since land 30 meters to drain, fluid behind metering valve 14 is vented via lines 80, 82, 84, 85 and 87. Spring 86 acting on the opposite end of throttle valve 14 causes the valve to move upward toward the closed position. Fuel flow then falls off at a rate dictated by spring 38, as shown by the slope of the droop line. It, therefore, will be appreciated from the above that the droop valve serves to produce droop type governing during this regime of opera tion.

As noted above, when flyballs 10 move outwardly as a result of an increase in speed being sensed, the pressure in line 20 increased. The fluid reaction surface 50 feels this increased pressure causing spool 42 to remain on stop 44. Land 32 of droop valve 26 also moved to the left uncovering its cooperating point so as to connect the space adjacent fluid reaction surface 52 to vent via lines 88 and 87. Hence, the control supplies the proper amount of fuel to hold the engine at its new steady-state operating point defined where droop lines intersect the new load Curve P. However, the decrease in fuel flow operates the engine at a new increase in r.p.m., and the integrating valve remained inoperative.

Next, consider the-case where the toad increases to the new load line designated by Curve N. Viewing FIG. 2, it is noted that the isochronous governor will then take over from the transitional line until the fuel is increased to the new point where the isochronous governor line intersects the new steady-state operating line N without an increase in speed. As the load increases, the speed tends to reduce so that flyballs 10, feeling this reduction in speed, tends to move inwardly rotating about pivot 14. This serves to position spool 16 to the left for reducing the area of orifice 18 and hence, reducing the pressure in line 20. Spring 38 of droop valve 26 repositions the droop valve spool 29 to the right since the pressure acting against fluid reaction surface feels a decrease in pressure. This has the immediate reaction of reducing the areadefined by metering land 30 to block off the flow, thereby reducing the flow of fluid draining from behind fuel valve 14. This, in essence, decreases the pressure drop across orifice 90 raising the pressure in line and in the space behind the throttle valve 14 for urging the throttle valve down to the open position for allowing more fuel to enter the engine.

Simultaneously, the pressure difference feit by reaction surfaces 50 and 52 increases in the direction to cause spool 42 to shift to the right. The reason that the pressure difference acting on reaction surfaces 50 and 52 increases is because spool 29, as mentioned above, had shifted to the right reducing the metering area controlled by land 32. Since this orifice is in series with orifice 60, the pressure drop across 60 decreases more than the pressure drop across 56; hence, the pressure in line 88 increases and the pressure in the space behind reaction 52 likewise increases more than the pressure on reaction 50. As spool 42 shifts to the right, the metering land 48 reduces the area of its cooperating port. Since this metering area serves to vent pressure from behind throttle valve 14 through lines 80, 82, 84, 90, 92 and 94, the reduced flow to vent decreases the pressure drop across orifice 90 raising the pressure in line 80 for causing the throttle valve 14 to move toward a more open position for increasing the amount of fuel to the engine. Hence, the droop valve which initially increased the fuel flow to the engine is complimented by the integrating valve which likewise increases fuel to the engine. This has the effect of shifting the droop line vertically along the insochronous governor line so as to change fuel flow without increasing the speed of the engine. When the new steady-state oper ating condition is met, namely, where the isochronous governor line intersects the steady-state operating line N, spool 29 of droop valve 26 will return to its original position and the integrating valve will be at a new position intermediate its stops 44 and 46. The integrating valve continues to translate until the droop valve is returned to its initial condition which sets the pressure in chamber 53 equal to 51. In order to achieve this, the speed error pressure in chamber 36 of the droop valve must have returned to its initial value and consequently speed must be equal to its initial value.

When the control is operating at a higher fuel flow at the 82 percent speed value and it intersects the upper transitional line, spool 42 of integrating valve 28 will bear against stop 46 and again the droop valve will take over the control for varying the fuel flow at the new speed condition.

Hence, it will be apparent from the above that during isochronous governing droop valve 26 will always seek an equilibrium position which may be designated at the point where A coincides with point A. The isochronous governor during the isochronous governing regime will be at various points intermediate the two stops. When the droop governor takes over control, the integrating valve will be urged against either of the stops and rendered inoperative so that the droop governor completely controls the engine along the various droop lines as indicated by FIG. 2. Of course, the 82 percent speed value was selected merely for illustration purposes but the same governing aspects are attendant regardless of the speed at which the governor is controlling. By virtue of locating the stops of the integrating valve at the proper points, it is possible to have isochronous and droop governing at the higher speeds, and reducing (to some degree) isochronous governing in lower speed regimes.

In the particular embodiment selected to illustrate this invention, the throttle valve 14 is shown as a spring loaded window type of valve that has a piston head sensing metered servo pressure for positioning the window-s for varying fuel flow. A suitable pressure regulator 100 indicated in blank regulates servo supply pressure being fed through line 108 to a constant value and the isochrOnous-droop governor varies pressure downstream of orifice 90 for positioning throttle valve 14. In certain applications particularly for jet engines, it is desirable to meter fuel as a function of an engine operating parameter such as compressor inlet pressure or compressor discharge pressure or the like as well as speed. In this light the pressure regulator 100 could be replaced by the device shown in FIG. 3.

The mechanism in FIG. 3 serves to create a hydraulic pressure whose value is directly proportional to the pneumatic pressure sensed by bellows 102. Pressure being sensed (either compressor inlet or outlet or the like of a jet-type engine (not shown)) through pipe 104 is admitted internally of the bellows for causing it to expand or compress as a function of the pressure being sensed. The free end of the bellows carries a servo valve 106 which meters supply pressure fed thereto through line 108 (note line 108 is identical to 108 in FIG. 1). The metered pressure in line 110 is admitted to cavity 112 to surround the bellows and on the underside of servo valve 106 via line 114. The forces felt by the internal effective area and the external effective area of the bellows will position the servo valve to an equilibrium point. When equilibrium is reached, the pressure fluid discharging from cavity 112 will be proportional to the pressure intern-a1 of the bellows. Of course, the cavity would be made to communicate with line 80 (FIG. 1) and orifice 90 would then be eliminated.

It will be appreciated that the fuel is used as the servo pressure fluid. A separate source of servo fluid may be used without deviating from the scope of this invention.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept as defined by the following claims.

We claim:

1. In combination with a speed responsive governor adapted to govern the speed of an engine, a control element controlling the speed of the engine and movable by application of fluid, means for controlling the application of fluid for positioning said control element in accordance with the governor speed so that each particular speed provides a predetermined different element position, means rendered operative at a selected speed to disable said controlling means and control the application of fluid for positioning said control element in various positions independent of any particular governor speed to maintain a constant engine speed.

2. In combination with a speed responsive governor for a turbine type of power plant, a control element controlling the speed of the power plant movable by the application of fluid, means responsive to an off-speed speed of said governor controlling the application of fluid for positioning said control element to maintain a constant speed of said power plant, means disabling said first mentioned means at a preselected element position for taking over the control of the application of fluid for positioning said element in accordance with the governor speed so that each governor speed has a corresponding element position.

3. An isochronous-droop governor for a turbine type power plant comprising, in combination, a speed sensing mechanism for developing a hydraulic pressure signal, means responsive to a preselected speed setting for modifying said sign-a1, a d-roop valve responsive to said modified signal for producing a first hydraulic pressure control signal, a control element responsive to said first hydraulic pressure control signal being positioned in accordance with the speed sensing mechanism so that a particular speed provides a predetermined element position, means including an integrating valve responsive to said hydraulic pressure signal rendered operative at a selected speed providing a second hydraulic pressure control signal to position said control element in various positions independent of said droop valve to maintain a constant power plant speed.

4. An isochronous-droop governor adapted to control the speed of an engine comprising, in combination, a speed sensing mechanism for developing a hydraulic pressure signal in accordance with the speed sensed, a control element, an integrating valve responsive to said pressure signal for positioning said control element to maintain a constant engine speed, means responsive to a preselected speed setting for modifying said hydraulic pressure, a droop valve responsive to said modified hydraulic pressure for disabling said integrating valve for positioning said element in accordance with the speed of the speed sensing mechanism so that each governor speed has a corresponding element position.

5. An isochronous-droop governor as claimed in claim 4 wherein said disabling means includes an adjustable stop limiting movement of said integrating valve in an element speed reducing direction.

6. An isochronous-droop governor as claimed in claim 4 wherein said disabling means includes an adjustable stop limiting movement of said integrating Valve in an element speed increasing direction.

7. An isochronous-droop governor as claimed in claim 4 wherein said integrating valve includes a ported casing, a piston slidably mounted in said casing, at least one fluid receiving chamber adjacent one end of said piston, flow passage means directing fluid through the port to said chamber, a first restrictor in said flow passage means upstream of said chamber and a second restrictor in said flow passage means downstream of said chamber, said first restrictor and said second restrictor serving to create a pressure in said chamber at some value proportionally less than said hydraulic pressure signal.

References Cited by the Examiner UNITED STATES PATENTS 9/1961 Clement 9148 1/1963 Stearns 72521 

1. IN COMBINATION WITH A SPEED RESPONSIVE GOVERNOR ADAPTED TO GOVERN THE SPEED OF AN ENGINE, A CONTROL ELEMENT CONTROLLING THE SPEED OF THE ENGINE AND MOVABLE BY APPLICATION OF FLUID, MEANS FOR CONTROLLING THE APPLICATION OF FLUID FOR POSITIONING SAID CONTROL ELEMENT IN ACCORDANCE WITH THE GOVERNOR SPEED SO THAT EACH PARTICULAR SPEED PROVIDES A PREDTERMINED DIFFERENT ELEMENT POSITION, MEANS RENDERED OPERATIVE AT A SELECTED SPEED TO DISABLE SAID CONTROLLING MEANS AND CONTROL THE APPLICATION OF FLUID FOR POSITIONING SAID CONTROL ELEMENT IN VARIOUS POSITIONS INDEPENDENT OF ANY PARTICULAR GOVERNOR SPEED TO MAINTAIN A CONSTANT ENGINE SPEED. 